The art of designing keels for sailing boats has progressed from weighted bulky structures as used on ancient reed boats and Columbian era boats to todays keel designs that employ aerodynamic fins.
Current fin keels are basically designed to achieve optimum laterial resistance with minimum drag and to optimize the aspect ratio of the keel so that the heeling forces are minimized. The resulting drag curve for these current designs is very steep at speeds between 5 to 8 knots. Therefore, the upwind speed is severly limited. In general, it can be said that prior art keels are designed primarily for boat stability rather than to achieve an increase in speed.
A search of the prior art did not disclose any patents that read directly on the invention. However, the following U.S. patents are considered related and indicative of the prior art:
______________________________________ PATENT NUMBER INVENTOR ISSUED ______________________________________ 768,085 Stromborg 23 August 1904 398,900 Martin 5 March 1889 367,771 Witmer 2 August 1887 ______________________________________
The Stromborg patent discloses a double-balancing safety-keel apparatus for use on sailing vessels. The apparatus is comprised of two vertically stacked fins or blades that pivot about a vertical axis located at the longitudinal center of the vessel. Each blade may be horizontally rotated on its axis independently of the other or both may be rotated or tuned simultaneously.
The Martin patent develops a steering gear apparatus for use on small sailing vessels. The apparatus is comprised of two in-line blades that are designed to be used both as rudders and centerboards. One blade is located at the aft end and the other at the forward end. Each blade may be extended or retracted independently of the other and the blades may be operated together or singularly. When the vessel is running before the wind, the forward blade would be retracted out-of-use leaving the aft blade to serve as the sole rudder.
The Witmer patent discloses a combined double-action steering and braking apparatus for use on sailing vessels. The apparatus is comprised of two retractable rudders, one located near the forward end and the other near the stem of the vessel. The posts of the rudders are connected by cross-cables so that both rudders may be operated simultaneously. When the rudders are turned, with respect to the centerline of the keel, they function as conventional steering rudders. However, when they are positioned normal to the keel a breaking action is produced.